Various types of superconducting active electronic devices have been proposed, typically utilizing Josephson junctions in which two layers of superconducting material are separated by a tunneling barrier. Such Josephson junction devices can be successfully formed from a variety of conventional superconducting materials (i.e., those which exhibit a superconducting transition temperature which can only be achieved with a liquid helium or liquid hydrogen coolant).
The more recently developed "high temperature" superconductors are ceramic type materials which exhibit a superconducting transition temperature significantly higher than the transition temperatures of classical superconductors. Hence, these materials may be cooled to their superconducting state by more economical coolants than liquid hydrogen or liquid helium. Such materials are not readily suited to construction of Josephson junction type devices. The relative instability of the currently available high temperature superconductors makes the fabrication of multi-layer structures difficult. The materials degrade upon contact with many substances and the annealing processes usually employed affect the superconducting characteristics of the materials.